1. Field of the Invention
The present invention relates to techniques for using viewing-angle-sensitive visual tags to determine the angular orientation and/or physical location of an object.
2. Related Art
Recent technological developments have made Global Positioning System (GPS) transceivers significantly cheaper and more portable. This has led to a proliferation of devices that use such GPS transceivers to determine physical location. For example, such devices include automobile navigation systems and GPS-enabled running watches.
Unfortunately, because of attenuation problems for GPS signals within buildings, these GPS-enabled devices are typically ineffective at determining physical locations inside buildings. Physical locations inside of a building can be determined by placing radio-frequency “beacon nodes” throughout the building. However, such beacon nodes are relatively complicated and expensive to deploy. Furthermore, these beacon nodes are likely to include batteries, which creates maintenance problems because the batteries need to be replaced at regular intervals.
It is also possible to use existing WiFi access points to determine the physical locations of objects inside a building based on the attenuation characteristics of WiFi signals within the building. However, determining locations in this way is not very accurate and requires potentially significant amounts of calibration effort. Furthermore, if furniture, access points, or even people move within a building, the system may require recalibration to effectively determine locations.
Another shortcoming of GPS systems is that they are not able to determine the angular orientations of objects. Such angular-orientation information can be useful in determining, for example, which direction a camera is pointing, or which direction an object is facing.
Hence, what is needed is a method and an apparatus for determining physical locations and/or angular orientations of objects without the limitations of the above-described techniques.